The invention relates to a process for the fabrication of electronic circuit elements and/or circuits in multilayer thick-film technology on a substrate, more particularly aluminum oxide or porcelain. The electronic circuit elements and/or circuits are printed onto the substrate in the form of liquid or pasty mixtures of materials, then heat-treated (to form a thick-film conducting layer) and, subsequently, at least one insulating layer is deposited on the thick-film conductor layer. The invention also relates to thusly produced electronic circuit elements and/or circuits in thick-film technology with a high degree of tolerance compliance.
To produce electronic circuit elements and/or circuits in thick-film technology, it is common practice to deposit thick-film conducting layer on a substrate consisting in particular of aluminum oxide or porcelain, a thick-film conducting layer by means of a screen or masking and template in the form of liquid or pasty mixtures of materials. The substrate is then subjected to a heat treatment, whereby the liquid or pasty mixtures of materials of the thick-film layer sinter out and the electrically conducting substrates contained in powder form therein are fixed on the substrate in the desired configuration. One or more insulating layers can be deposited on the thick-film conducting layer thus produced.
The following publication has been cited as relevant prior art: D. J. Holmes and R. G. Loasby: Handbook of Thick-Film Technology, Electrochemical Publicationi Ltd., Ayr, Scotland, 1976, Bell and Bain Ltd., Glasgow 1976.
It is likewise common practice to produce thermoboards in this fashion for printing presses, whereby an electrically conducting resistive layer is deposited using thick-film technology directly on the substrate and, again, an insulating layer is deposited thereon.
It is common practice, e.g., when making thermoboards, to trim the individual resistors of the resistive layer until each individual resistor attains the desired resistive value in a defined tolerance range. To date, it has merely been possible to trim the individual resistor in terms of its volume merely by changing the surface configuration, which results in a number of disadvantages. By changing the printing surface of the individual resistor, the whole printing pattern changes for the worse. Furthermore, this kind of trimming is not very accurate and requires relatively wide resistive tolerance ranges. Sand blasting as an abrasive technique for the surface is only possible for large surfaces. It cannot be used in a meaningful way to produce this type of resistors. In addition, in this case the corners are broken, with the result that the individual type face of the resistance spot becomes less sharp.
Another drawback of the processes of the prior art exists for the production of these thick-film circuit elements and/or circuits. It is not possible to print by fine-line technique and with a high degree of tolerance compliance in different planes above the substrate, i.e., again to deposite a thick-film conducting layer on an insulation layer that has been deposited. To date, only approximate results have been achieved, e.g., the placing of conductor tracks in different planes insulated from one another by insulating layers. It is not possible, however, to print any desired component, e.g., an IC or a resistor, in any desired plane above the substrate.
Likewise, if hybride circuits are designed as, thermal printing boards the necessity of depositing the resistor layer directly on the substrate is also a disadvantage, because most of the heat generated in the resistors is dissipated to the substrate and, hence, is no longer available for its actual task, i.e., the printing of the paper. Therefore, thermoboards of prior construction require considerable power in order to produce a satisfactory printing pattern. Likewise, the layer of resistors must be coated with an insulating layer, preferably a glass layer, to prevent the resistor layer from being scuffed prematurely when the paper enters the press. However, this deteriorates the layer of resistors still further and, on account of the insulating layer, again considerable power is required for printing the paper. As a result, a greater contact pressure is needed at the interface of the thermal printing boards and the paper to be printed.